1. Field of the Invention
This invention relates to a manufacturing method of a silicon carbide semiconductor apparatus such as a high-power silicon carbide vertical MOSFET.
2. Description of the Related Art
In a manufacturing method of a silicon carbide MOSFET (Metal Oxide Semiconductor Field Effect Transistor) which is a kind of silicon carbide semiconductor apparatus, it is necessary to make a channel length uniform to make a threshold voltage even in order to obtain the silicon carbide MOSFET with the same on resistance.
In a manufacturing method of a related-art silicon carbide semiconductor apparatus in order to obtain a uniform channel length, a channel region is formed in the portion in which an inorganic material mask pattern is widened in a self-alignment manner by forming the inorganic material mask pattern on a silicon carbide substrate, implanting a first conduction type impurity ion, forming an inorganic material film on the inorganic material mask pattern and its etch back, and implanting a second conduction type impurity ion in order (for example, JP-A-2006-128191, pages 9 to 13).
Also, in a manufacturing method of a related-art conventional thin film transistor, as a method for forming an LDD (Lightly Doped Drain) part in a self-alignment manner, there is a method wherein after a resist pattern in which a width of the base is larger than a width of the top is formed on a film used as a gate electrode, the film used as the gate electrode is removed and a high concentration ion is implanted and a part of the thickness of the resist pattern is removed by dry etching and the film used as the gate electrode is removed and a low concentration ion is implanted in order (for example, JP-A-2002-343810 (pages 4 to 6).
In the manufacturing method of the related art silicon carbide semiconductor apparatus as described in JP-A-2006-128191, the whole surface of the inorganic material film is etched back in order to widen the inorganic material mask pattern, so that shapes of the portions in which the inorganic material mask pattern is widened vary. Then, as compared with the inorganic material mask pattern before widening, the edge portion of a cross-sectional shape rounded or an angle of inclination of the side portion does not become constant and lengths of widening of basal portions vary. Thus, the inorganic material mask pattern cannot be widened with a cross-sectional shape changed in a conformal mapping manner from the inorganic material mask pattern before widening, so that there is a problem that a width of a channel region formed in the widened portion does not become constant and on resistances vary.
Also, when a method for decreasing a width of a resist mask by removing a part of the thickness of the resist pattern in which a width of the base is larger than a width of the top by dry etching as described in the manufacturing method of the related-art thin film transistor is applied to a self-alignment formation method of a channel region of a silicon carbide semiconductor apparatus, a problem that a surface of a silicon carbide layer which is not covered with the resist pattern is exposed to plasma and thereby an electric charge due to plasma damage occurs on a surface of a silicon carbide film used as the channel region and a threshold voltage of the silicon carbide semiconductor apparatus varies might arise.